SUMMARY/ABSTRACT The lack of effective glioblastoma treatments poses a significant health problem and highlights the need for novel and innovative approaches. Immunotherapy is an appealing strategy because of the potential ability for immune cells to traffic to and destroy infiltrating tumor cells in the brain. New information suggests that patients mounting immune responses after immunotherapy preferentially recognize novel neoantigens created by tumor-specific mutations. Our data, and that from other immunotherapeutic strategies for patients with cancer, suggest that the vast majority of tumor-specific T cells induced by such personalized, patient-specific immunotherapies do NOT recognize well-characterized, known antigens. Such information is consistent with recent data from other immune-responsive cancers, such as melanoma, in which the percentage of tumor-specific T cells recognizing known antigens was less than 1%. In order to design the most effective immunotherapeutic strategies for glioblastoma, we believe that it is critical to understand which antigens tumor-specific T cells recognize in this disease. Our hypothesis is that glioblastoma patients treated with immunotherapy will mount anti-tumor immune responses against specific mutations and splice variants in their individual tumors. Similarly, our other recent findings strongly suggest that the addition of PD-1 antibody (mAb) blockade to DCVax enhances both the intra-tumoral CD8+ T cell response and clinical benefit in pre-clinical studies. Furthermore, the timing of PD-1 mAb blockade is immunologically relevant; our unpublished, recent clinical trial results highlight how the neoadjuvant (prior to surgery) treatment with PD-1 mAb blockade induces enhanced anti-tumor immune responses and clinical benefit. We hypothesize that the addition of PD-1 mAb blockade should amplify the neoantigen-specific T cell response induced by DC vaccination, both in the blood and the tumor. To test these important questions, In Aim 1, we will develop a new bioinformatics pipeline to predict neoantigens that arise specifically from the types of genetic alterations that occur in GBM. In Aim 2, will create immunocompetent murine glioma models to test the importance of neoantigens. Finally, in Aim 3, we will identify neoantigen-specific T cells from both the TIL population and peripheral blood of GBM patients treated with immunotherapy. These studies span the continuum of translational research in brain tumor immunotherapy and will likely provide informative new insights for the development of new, rational immune-based strategies for brain tumor patients.